Role of nitrite reductase in N2O production under aerobic conditions: An index for predicting the intensity of N2O production

To verify the feasibility of using nitrite reductase (Nir) activity as an indicator for predicting nitrous oxide (N2O) production under aerobic conditions, an A/O SBR under different aeration intensities was applied. Firstly, by analyzing Nir activities and chemical substances, the main source of N2O was recognized. Secondly, the relationship between Nir activities and N2O production was determined. Finally, the influences of aeration intensities on N2O production and Nir activity were examined. Results showed that denitrification occurred under aerobic conditions was the main N2O production process other than that anoxic condition. Variations of the Nir activity reflected the change in the overall concentration of N2O and had a positive correlation with theN(2)O production (r = 0.509, n = 31, P = 0.003 <0.01). The Nir activity can be used as an indicator to characterize changes in N2O emissions. The N2O emission and its proportion (1.2%) in nitrogen loss were least when aeration intensity was 0.8 L.min(-1). The Nir activities (0.81 +/- 0.03 U.mL(-1)) were relatively high when aeration intensity was 0.6 L.min(-1). In addition, The Nir activity had a high affinity for nitrite and was not directly affected by DO (r = -0.333, n = 17, P = 0.191 >0.05).